Tarsier
(Varies by Species)

Found in the forests of Southeast Asia, the Tarsier has the largest eyes relative to body size of any mammal on Earth — and unlike most animals, it cannot move them within their sockets at all. To compensate, its head can rotate nearly 180 degrees in each direction allowing it to see almost a full 360 degrees, owl-style, to scan its surroundings. Each of those enormous eyes is actually larger than the animal's entire brain!